The invention relates to a device for coating substrates with a material vapor in negative pressure or vacuum.
The field of the invention is thus coating of substrates, for example, foils, plates or shaped parts. There are various methods to coat such substrates. On the one hand, there is the possibility to vaporize neutral particles thermally which will then deposit on the material to be coated. As a further possibility there is sputtering. Also, there is a method of depositing ionized particles onto the surface to be coated whereby for this purpose an electrical field between an anode and a cathode is produced in which the ionization of particles occurs in a plasma. It is, in general, known that for generating thin layers in vacuum an ionization of the material vapor results in improved coating properties. Especially the adhesion and the compactness of the layers can be improved considerably. Furthermore, there is the possibility of a reactive deposition. The ionization of the material vapors can be achieved by electrical discharge, whereby a differentiation must me made between glow discharge and electric arc discharge. The invention is based on the latter method.
From German Offenlegungsschrift 42 00 429 a coating device is known in which thermally produced material vapors are ionized by anodically determined vacuum electric arc. The basic principle is that the vaporizing device is used for producing the material vapor and also as an anode wherein the crucible in which the material vapor is produced is switched as the anode. This known device has the advantage that for maintaining the electric arc no process gas is required, however, the known coating device has a considerable number of disadvantages. For example, it is disadvantageous that the electric circuit of the thermal vaporizer is coupled to the electric circuit of the electric arc so that they affect one another in a detrimental manner. For example, in a crucible through which current flows high magnetic fields are generated such that the current flow between the crucible (anode) and the cathode is made so difficult that ionization and thus anode activity no longer takes place or only to a very limited extent. The arc is thus very instable. A further disadvantage is the parallel switching of the ohmic resistance of the crucible with the plasma resistance across the crucible. When the plasma resistance is of the same magnitude as the crucible resistance, the effective ohmic crucible resistance is reduced. Thus, the ionization and the vaporization rate are coupled tightly with one another which greatly limits the optimization of the coating via ionization and vaporization rate. A further disadvantage is finally the spatial fixation of ionization onto the crucible area because the crucible functions simultaneously as the anode.
From German Offenlegungsschrift 42 17 450 an ion plating method as well as a corresponding ion plating device with a material vapor source in a hood-like ionization chamber and with an electrically separately supplied electron gun, the beam of which enters the hood via a lateral opening and vaporizes the material contained within the container. This device is used for ionic vapor deposition on metal bands.
In East German patent 145 283 a method for generating wear-resistant and corrosion-resistant layers on metallic workpieces by ion treatment in vacuum is disclosed. The device comprises a material vaporizer as well as, in a perpendicular arrangement thereto, an ionization source. Furthermore, a supply device for reactive gases is provided. The power sources for the vaporizer and the ionization source are electrically separate from one another. The device is used for reactive ion vapor deposition of wear-resistant hard material coatings.
From Swiss patent 683 776 a device for continuous ion vapor deposition on packaging foil strips is disclosed. The device is comprised of a material vaporizer with correlated electron gun as well as an ionization device employing a hollow cathode low voltage electron gun, the beam of which is guided perpendicularly to the vapor stream. The power supply is also provided by separate electric sources.
U.S. Pat. 4,336,277 discloses a device with an ionization device comprised of an anode and a glow cathode for producing an ionized electron beam as well as a material vapor source. An electric separation with separate current supplies is provided for the vaporizer and the ionization device. The device is used for reactive ion vapor deposition.
In U.S. Pat. 4,692,230 a device for sputtering stacked layers is disclosed. It also includes an electrical separation of the material vapor source in the form of a magnetron sputtering cathode and of the ionization device comprised of a glow cathode and anode.
In U.S. Pat. 3,482,133 a source for generating ions or electrons is disclosed whereby with the aid of the ion or electron beam a ceramic material is vaporized. The charge support source comprises a cathode in the form of a thin metal plate as well as a metal net arranged in front thereof and acting as the anode.
It is an object of the invention to provide a coating device in which a mutual disturbing effect of the supply current circuits is prevented and the parameters deposition rate and ionization degree can be adjusted independent of one another while maintaining a stable arc discharge between the anode and the cathode.